Vacant TV band channels, also known as “TV white space”, are ideally suited for unlicensed wireless communications services. Access to vacant TV band channels facilitates a market for low-cost, high-capacity, mobile wireless broadband networks, including emerging in-building networks. Using TV white space, the wireless broadband industry can deliver wireless communications services to households and handholds at an inexpensive rate. However, as the TV band spectrum “belongs” to TV broadcasters, any secondary usage must necessarily be conditional. Therefore, the United States Federal Communications Commission (FCC) engineering office released a Report and Order (FCC R&O) on Nov. 14, 2008, that spelled out the conditions which TV band devices must satisfy in order to use the TV white space. Currently under consideration is construction of a database for assisting the TV band devices in locating TV white space that can be used for secondary wireless services. The main requirement is not to interfere with the primary wireless services active in any given geographical area. Thus, the signals broadcast by any TV band device operating in the TV white space must follow the FCC R&O so that the quality of the primary wireless services, such as digital television (DTV) broadcasts, wireless microphone systems, or other emerging licensed services already deployed, or to be deployed, will not be degraded by signals transmitted by the TV band devices. The term “white space etiquette” is used for the regulations that must be taken into account when designing and using devices adapted to operate in the TV white space. For conformity with these requirements, FCC R&O specifies several requirements, of which the 4 most relevant are summarized below.
Capability: For compliance with this requirement, FCC mandates that both fixed and mobile white space devices include geo-location and sensing capabilities and use a database, referred to herein as the “white space (WS) database”, which provides information regarding the primary services active in each TV market. The WS database includes TV channel allocation and location of principal venues, such as stadiums, electronic news groups (ENGs), theatres, churches, etc. that operate wireless microphone systems. The database access and sensing capabilities should enable TV band devices to share TV white space with other secondary services without interfering with primary services. Personal/Portable TV band devices must either be under the control of a fixed TV band device, or must employ geo-location and/ or database access and spectrum sensing capabilities. When a protected signal is detected in a TV channel being used by a TV band device, the TV band device must cease operation in that TV channel within 2 seconds.
Power Radiation: FCC R&O specifies a maximum transmission power for fixed TV band devices of up to 1 watt with an antenna gain of 4 watts equivalent isotropic radiated power (EIRP). Personal/portable TV band devices are permitted to radiate up to 100 milliwatts EIRP with no antenna gain. When operating on a TV channel adjacent to a protected TV channel, the power radiation shall be limited to 40 milliwatts EIRP.
TV channel Assignment: Fixed and portable TV band devices can operate on any vacant TV band channel, from TV channel 21 to TV channel 51, excluding TV channel 37 which is reserved for telemetry. Communication between two fixed TV band devices is also allowed on TV channel 2 and TV channels 5 to 20, except those used by the private land-mobile radio services for public safety.
Adjacent TV channel Limitation: Fixed TV band devices are not allowed to operate on TV channels immediately adjacent to an ATSC protected TV channel. Portable TV band devices are allowed to operate on a TV channel immediately adjacent to a protected TV channel, but their out-of-band emission on the side of the adjacent TV channel should be limited to 55 dB below the power level at which they operate.
The wireless industry is contemplating using the TV band white space by developing standards for technology convergence into an architecture that is comfortable, easy to use and attractively priced. For example, the IEEE 802.22 Working Group, formed in 2004, received a mandate to develop a standard for Wireless Regional Area Networks (WRAN). The goal of this standard is to provide rural area broadband services to single-family residential, multi-dwelling units, small office/home office, small businesses, etc. The standard will be used by license-exempt devices that operate in the TV white space and conform to the FCC R&O. The draft of the 802.22 standard specifies that the network should operate in a point to multipoint configuration, where a base transceiver station (BTS) or an access point (AP) controls the medium access for all customer premise equipment it serves, while avoiding interference with broadcast services present in the operating area. One key feature of the WRAN BTS/AP is the capability to perform distributed spectrum sensing, where the customer premises equipment senses the spectrum and sends periodic reports to the serving BTS/AP informing it about what has been sensed. Based on the information gathered, the BTS/AP determines whether the current operating channel must be changed.
Conceptually, a TV band device should be capable of sensing its environment and location and altering its power, frequency, modulation and other parameters to dynamically use TV white space. TV band devices should allow spectrum sharing on a negotiated or opportunistic basis, adapt spectrum use to the real-time conditions of the operating environment, offer the potential for more flexible, efficient and comprehensive use of available spectrum, and reduce the risk of harmful interference. In general, a TV band wireless system may have 4 major components, i.e. a Sensing and Database Engine (SDE), a Physical Layer Processor (PHY), a MAC processor and a Spectrum manager 50a(SM).
Spectrum sensing and WS database engine (SDE) operates to detect incumbent signals generated by primary services such as TV signals and wireless microphone systems. Significant effort has been invested in drafting the 802.22 Standard, including contributions on both ATSC signal sensing and wireless microphone sensing. Several key algorithms were developed and tested, based on various characteristics of the signals, such as signal energy detection, correlation, cyclostationary feature extraction, eigenvalue decomposition, fine FFT etc.
For ATSC signal sensing, detection is based on the ATSC signal format, which includes known embedded bit sequences, namely the ATSC pilot and pseudo-noise (PN) sequences. As such, various solutions are being proposed by 802.22 contributors. However, the hardware implementation of a sensor/detector still presents significant challenges due to lack of affordable, low-cost front-end components. Today, most proposed designs involve modifying the current TV tuner design to enable it to handle a required −114 dBm sensitivity. However, current consensus on ATSC signal sensing is that the FCC Rules and Orders may not meet broadcasters' real requirements. Namely, the broadcasters provide contours of the TV channels they operate, while the FCC Rules and Orders require that TV band devices use sensing to ensure that they do not interfere with TV channels operating in their area. However, it is quite possible that a TV band device will fail to sense a TV signal even if it is located within the contour of a TV channel licensed in that area. This could occur if the TV station is not broadcasting on that TV channel at the time. Broadcasters do not permit others to use their spectrum, even when it is not in use. Alternatively, if the sensing engine is located inside a building where a TV signal is not detectable (e.g. in the basement of a building) the broadcast may not be detected by the TV band device.
Sensing/detecting a wireless microphone signal is an even more complex operation. This is partly because there is no universal standard for wireless microphone systems. For example, wireless microphones may use UHF or VHF frequencies, frequency modulation (FM), amplitude modulation (AM), or various digital modulation schemes. More advanced models operate on a user selectable frequency to avoid interference, and permit the concurrent use of several microphones. For the wireless microphone systems that use frequency modulation, the FM waveform has an energy concentration about 40 kHz which may drift around within a 200 kHz bandwidth. However, the wireless microphone signals do not have any known sequence and the detection threshold based on the signal energy has been set very low (at −114 dBm). This makes the detection extremely challenging, and there are no proven solutions or viable proposals available yet. One solution proposed by the IEEE 802.22 Working Group in 802.22 TG-1 is to add a beacon mechanism to the wireless microphone signals, which should facilitate wireless microphone sensing. However, this solution is not ideal, since it is impractical to retrofit existing wireless microphones with a beacon mechanism.
The IEEE 802.22 Working Group also proposed use of WS database servers with WS databases for storing all meaningful system information and policy related radio parameters, to assist operation of TV band devices in a given area. The information stored in these WS databases would include the number of the protected TV channels, geo-location and TV channel contours of each TV tower and each stadium or other site using a wireless microphone system, and terrain elevation for the service region, maximum EIRP for the licensed TV channel, antenna height and gain, propagation models, interference scenarios. The information in the WS database will also include identification and geo-location information for the fixed TV WS (white space) devices in the service area, their transmission power and operating TV channels, etc. It is expected that the type and extent of information stored in the WS database will be agreed upon by broadcasters, regulators and service providers, and will be updated regularly. The WS database should be pulled by the TV band devices or pushed to the TV band devices. It is also expected that such WS database servers would be provided to serve each local network and that a regional WS database may also be available. The term “system information” is used to designate the information stored in the WS database.
FIG. 1 illustrates relationships and interactions between entities that operate, use and maintain a WS database 10 using a WS database server 12, Broadcasters 14 and regulators 16 (or their authorized representatives) are the owners of the WS database server 12 and the WS database 10; users of the WS database 10 are TVWS service providers 18 and TV band device users 20. This system is organized in a client-server architecture where the WS database server 12 is the central registering unit, as well as the only provider of content and service. The remaining entities, TVWS service providers 18 and TV band devices 20 can only request content or the provision of services, without the possibility of sharing any of their own resources.
Broadcasters 14 and regulators 16 provide an identification of the available TV channels (i.e. by TV channel number) and an identification of the protected TV channels in their service area, with associated service contours. The owners 14, 16 must regularly update the WS database 10 with any new information available to them. They also perform any authorization, authentication and administration (AAA) functionality.
The TV WS service providers 18 and the TV band devices 20, which are the WS database 10 users, shall provide their configuration/transmission parameters to the WS database, together with any sensed data regarding the presence of a primary service they may have identified (sensed, detected) in that area. As users of the WS database, these entities 14, 16 must be validated (authentication and authorization) upon requesting WS database access. The information downloaded by these users is submitted to a validation and security verification process; the broadcasters 14 and/or regulators 16 shall confirm data before updating the WS database 10. TV band devices 20, particularly base transceiver stations (BTS) and access points (AP), shall access the WS database 10 to acquire protected TV channel information, available TV channel information, interference status, power limitation data, etc, which is used to configure spectrum usage, and convey that information to any TV band device 20 under their control . Each time an AP or BTS receives updates from the WS database 10, TV band devices 20 should reconfigure their spectrum information within 30 seconds, For example, when a broadcaster decides to use a TV channel, that TV channel must be vacated within a 30-second time frame.
Broadcasters 14 and regulators 16 may push updates to all TV band devices 20 in the service area either directly or via the TV WS service providers 18. Preferably, the TV WS service providers 18 provide an anchor point where the WS database server 12 can push data. Broadcasters 14 and regulators 16 may push/update a particular data type to clear a TV channel or multiple TV channels within a certain time. Many control networks and network entities and for managing TV white space spectrum usage by wireless radio access networks have been described. However, those control networks and network entities are based on a client-server architecture, which are expensive to implement, requires extensive maintenance, and is susceptible to single point of failure.
There therefore exists a need for a control network for a wireless radio access network that is robust and inexpensive to implement.